Table 1.

Comparison of WHI and NHIRD study designs

Study protocol	WHI RCT		NHIRD
Study enrollment	1993–1998		1997–2000
Study dates	E+P	1993–2002*	1997–2007
	E only	1993–2003*
Participant age at enrollment	50–79		50–79
Menopausal status	No vaginal bleeding for 12 months		Assumed menopausal based on age ≥ 50
Controls	RCT 1:1 randomization		Age-matched 1:2
Exclusion criteria**	Medical condition associated with predicted survival < 3 years***
	Prior breast cancer
	Prior other prior cancers within 10 years
	Endometrial hyperplasia
	Alcoholism, drug dependency
	Dementia, mental illness
	Acute MI, CVA, TIA within 6 months
	Severe hypertension
	Chronic hepatitis or cirrhosis
	Prior PE or DVT
Exposure	E+P	CEE 0.625 MPA 2.5 mg	CEE 0.625, MPA 5 mg
	E-only	CEE 0.625 mg	Same
Duration of exposure median (range)	E+P	cumulative drop out 42%	0.57 years (0.15–9.8)
	E-only	cumulative drop-out 54%	0.76 years (0.15–10.3)
Duration of follow up mean (range)	E+P	5.2 years (3.5–8.5)	9.5 (0.1–10.6)
	E-only	6.8 years (5.7–10.7)	9.4 (0.1–10.6)

^*Post-intervention phase 2002–2005

^**WHI exclusionary criteria not available in the NHIRD: abnormal pelvic exam, hysterectomy

^***AIDS, COPD, CHF, ESRD